1. Field of the Invention
The present invention relates to an etching method and a substrate processing apparatus.
2. Description of the Related Art
Magnetic Random Access Memory (MRAM) is a memory that uses a magnetic tunnel junction (MTJ), which is basically made of a laminated film having an insulating layer arranged between two magnetic layers. An MRAM element may be made of a multilayer film material that includes a metal thin film containing cobalt (Co), for example.
The boiling point of the metal thin film exceeds 1000° C., and as such, etching of the metal thin film is typically performed by sputtering. However, in recent years, techniques for dry-etching the metal thin film of the MRAM element are being proposed. For example, Patent Document 1 discloses a method for dry-etching a metal thin film of an MRAM element using an etching gas containing chlorine gas (Cl2) or fluorine gas (F2).
However, when the metal thin film is dry-etched using an etching gas containing chlorine (Cl2) gas or fluorine (F2) gas, reaction products containing chlorine (Cl) or fluorine (F) are generated during the etching process. Reaction products containing chlorine (Cl) or fluorine (F) are less likely to be vaporized and are more likely to remain in the processing chamber. Thus, as a result of etching the metal thin film, reaction products may be accumulated on a wall face of the metal thin film of the multilayer film such that the shape of the lower layer films may be degraded. Also, it may be difficult to remove the reaction products from the etching surface owing to their tendency to resist vaporization, and as a result, it may be difficult to control the etching process to achieve desired critical dimensions (CD), for example.
For example, in the case where the metal thin film contains cobalt (Co), when the metal thin film is dry-etched by an etching gas containing chlorine (Cl2) gas or fluorine (F2) gas, reaction products containing cobalt (Co) and chlorine (Cl) or fluorine (F) may be generated during the etching process. Note that the boiling point of a compound of cobalt (Co) and chlorine (Cl) is 1049° C., and the boiling point of a compound of cobalt (Co) and fluorine (F) is 1400° C.
When the boiling points of the compounds are relatively high as described above, the reaction products generated during the etching process are less likely to be vaporized and are more likely to remain in the processing chamber. Note that to perform an etching process efficiently, it is important to select a suitable etching gas such that reaction products generated during the etching process have relatively low melting points and boiling points that would enable the reaction products to be vaporized immediately and discharged.